The present invention relates to an electric compressor, and more particularly, to the cooling and leakage current prevention of coils wound around a stator.
An electric compressor includes a housing, a compression mechanism, which is accommodated in the housing, and an electric motor, which drives the compression mechanism. The electric compressor is installed in a vehicle and arranged in a refrigerant circuit of an air conditioner. The influence of leakage current from the electric compressor on electric devices, control devices, and the like that are installed in the vehicle should be decreased.
When an electric compressor stops operating, liquid refrigerant in the refrigerant circuit is apt to enter the housing through a suction port of the electric compressor and collect in the housing. The liquid refrigerant contains lubricant. As the amount of collected liquid refrigerant increases, coils wound around a stator of the electric motor become immersed in the liquid refrigerant. When the coils are immersed in liquid refrigerant, the permittivity of the liquid refrigerant lowers the insulation between the coils and the stator and between the coils and the housing, to which the stator is fixed. This increases the leakage current that flows to the stator and the housing. Thus, in the electric compressor, leakage current should be prevented when the electric compressor is stopped and the liquid refrigerant collects in the housing. A highly insulative lubricant (e.g., POE oil) may be used in combination with the refrigerant to suppress leakage current. However, when a substance having low insulation enters the electric compressor, leakage current cannot be suppressed even when using a highly insulative lubricant. Further, lubricant having low insulation (e.g., PAG oil) may be used depending on the specification of the electric compressor. In such a case, leakage current cannot be suppressed.
Japanese Laid-Open Patent Publication No. 2002-227767 discloses an electric compressor that suppresses leakage current. In this compressor, when voltage is applied to the electric motor, the lubricant collected on the electric motor produces leakage current. More specifically, when the dissolution rate of refrigerant in the lubricant increases, the amount of refrigerant, which has a large relative permittivity, dissolved in the refrigerant increases and thereby produces a large leakage current.
The above publication discloses two ways to suppress leakage current. One way is to form a resin molding serving as an insulator between a stator core and coils to envelop the teeth of the stator core and/or the coil ends of the coils. Another way is to form a resin molding serving as an insulator that entirely envelops the coils. In this manner, the invention of Japanese Laid-Open Patent Publication No. 2002-227767 is a resin insulator molding that improves insulation. This reduces leakage current even when refrigerant collects on the teeth and coil ends.
During the operation of the electric compressor, the coils wound around the stator are heated. This may deteriorate the coils. Further, the heat may affect a power supply unit and control unit of the electric motor that are arranged on the periphery of the electric compressor housing. Thus, in conventional, the stator and the coils of the electric motor are accommodated in the housing of the electric compressor and the refrigerant that circulates through the housing is used to cool the stator and coils of the electric motor. However, the invention of Japanese Laid-Open Patent Publication No. 2002-227767 uses a resin molding to envelop the coil ends or the entire coils and prevent contact between these parts and lubricant in which refrigerant is dissolved and thereby suppress the generation of leakage current. This insulates the coils and the housing but completely isolates the coils of the electric compressor from the circulating refrigerant. In this structure, the influence of heat from the coils cannot be prevented.